Plasterboard is a building board used inside a house to make walls and ceilings. It comes in large flat sheets: thick paper on the outside, plaster in the middle. Builders fix the sheets to a wooden or metal frame, fill the joins, then paint. It is faster than spreading wet plaster over a whole wall. In British English this is the usual word. In American English people often say drywall, or Sheetrock, which is a brand name that spread into everyday speech. It is a practical, trade word, not a poetic one.